(1) Field of the Invention
The present invention relates to a holding assembly that holds a portable power tool, such as an electric driver that is used in the assembly of electrical appliances.
(2) Description of the Prior Art
Electrical appliances are often assembled on an assembly line by arranging personnel along a conveyor that carries goods. One task frequently performed during assembly is the tightening of screws, with power tools such as electric drivers being used to complete this task in a short time. Such electric drivers are often held by a holding assembly that may be attached to the factory ceiling, for example.
A reel-type assembly is commonly used for holding power tools. Such assembly includes a reel that is fixed at a given position, such as to the factory ceiling, and a rope that is wound around the reel. An electric driver or other power tool is attached to the rope and is usually held at a standard position above the operator's work area. To use the electric driver, the operator pulls the tool down by hand.
Reel-type holding assemblies have a disadvantage in that the electric driver is merely suspended on a rope, so that the reaction force produced by the screw tightening torque of the electric driver when the screw has been tightened needs to be countered by the operator's hands. This requires a noticeable exertion by the operator, and so can prevent an operator from continuously working for a long time.
In view of the stated problem, Japanese Laid-Open Patent Application H07-1347 teaches the power tool holding assembly shown in FIG. 1.
The holding assembly shown in FIG. 1 is a crank-type holding assembly. This holding assembly comprises a main post, a first arm that is attached to the main post so as to be freely rotatable in the horizontal plane, and a second arm that is connected to the first arm so as to be freely rotatable in the horizontal plane. This holding assembly is used with the electric driver attached to the end of the second arm. The second arm is composed of a quadric-linked construction where an extension spring is extended between opposite corners of the construction.
When performing a screw tightening operation using an electric driver supported by the above crank-type holding assembly, the operator first holds the grip of the electric driver and moves the electric driver in the horizontal plane to position it above the screw tightening position. The operator then pulls the electric driver down against the tension of the extension spring to move the driver bit to the screw tightening position, and performs the screw tightening operation. When doing so, the reaction force to the screw tightening torque of the electric driver produced when the screw has been tightened is largely absorbed by the holding assembly. This greatly reduces the exertion required of the operator.
When using a crank-type holding assembly, however, if the operator releases the driver on completing the tightening of one screw, the tension of the extension spring will pull the electric driver upward. As a result, the operator has to go to the trouble of pulling the electric driver down by a considerable distance to tighten each screw, making the screw tightening process inefficient.
Also, when the operator moves the electric driver in the horizontal plane to position it above the screw tightening position, the first arm will move in a circle about the join with the main post and the second arm in a circle about the join with the first arm. Since a combination of these circular movements determines the trajectory of the electric driver, the operator can move the electric driver with great freedom. Accordingly, when moving the electric driver to the intended position, the operator will try to use the shortest possible course. This means the operator will attempt to move the electric driver directly to the intended position.
As described above, however, linear movement of the electric driver involves circular motion of the first and second arms. This means that the direction moved by the electric driver does not correspond to the directions moved by the first and second arms. Inertia in the first and second arms affects the movement of the electric driver, and the directions in which inertia acts in the first and second arms can differ to the direction of movement of the electric driver. This means that the operator can find the power tool being pulled in an unintended direction. Such unintended movement prevents the operator from quickly and correctly positioning the power tool at the required position.